1. Field of the Invention
The present invention relates to a diversity reception technology for wireless systems using a direct spread spectrum communication method.
2. Description of the Related Art
In mobile communications, fading occurs in a multipass environment. If fading occurs, the received input is subjected to significant level fluctuations and phase fluctuations of several tens of dB. As a result, a code error frequently occurs in digital transmission. Diversity reception methods were suggested as a fading countermeasure. Among such methods, antenna switching diversity is suitable for wireless systems requiring simplification of system structure, such as mobile stations. Japanese Patent Application Laid-open No. 2003-46418 disclosed a technology by which in a wireless system using spread spectrum communication, antenna switching is conducted by comparing a threshold value and an average maximum correlation value which is output by a matched filter, per 1 frame, thereby enabling diversity communication with excellent SNR (Signal to Noise Ratio). This technology is more effective than the method using RSSI (Receive Signal Strength Indicator) with respect to resistance to wave interference and even more effective in a band where a large number of wireless systems are co-present, for example, an ISM band (2.4 GHz band).
However, with the above-described prior art technology, it was impossible to predict the fading fluctuations and to conduct antenna switching before the reception signal level drops. In wireless communication under fading environment, it is important to predict fading fluctuations in advance and to conduct antenna switching before the reception signal level drops.